// Problem: 
// Contest: 
// URL: 
// Memory Limit: 
// Time Limit: 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
int n;
int C(int a,int b)
{
	int ret=1;
	for(int i=a,j=1;j<=b;i--,j++)
	{
		ret=ret*i/j;
		//if(ret>n)return ret;
	}
	return ret;
}
signed main()
{
	int t=1;
//	cin>>t;
	while(t--)
	{
		cin>>n;
		if(n==1)
		{
			printf("1");
			return 0;
		}
		for(int i=16;i>=0;i--)
		{
			int l=2*i,r=1e9,mid,mv;
			while(l<r)
			{
				mid=(r-l)/2+l;
				mv=C(mid,i);
				if(mv==n)
				{
					cout<<(mid+1)*mid/2+i+1;
					return 0;
				}
				else if(mv<n)
				{
					l=mid+1;
				}
				else
				{
					r=mid;
				}
			}
		}
	}
	return 0;
}
